1. Field of the Invention
This invention relates to a tape cassette and a metal mold device for molding tape cassette halves designed for housing therein a tape-shaped recording medium, such as a magnetic tape. More particularly, it relates to a tape cassette made up of a pair of cassette halves part of which is formed by a metallic plate, and to a metal mold device for molding the cassette halves of the metal mold.
2. Description of the Related Art
Up to now, a tape cassette housing therein a magnetic tape having a tape width of 8 mm has been used for recording data processed by a video tape recorder recording video signals or a computer.
A tape cassette used as a recording medium for a video tape recorder is configured as shown for example in FIG. 1. Such a video tape cassette 100, abbreviated herein to a tape cassette, is comprised of a rectangular main cassette portion 101 made up of a pair of cassette halves, namely an upper cassette half 102 and a lower cassette half 103, as shown in FIGS. 1 and 2. On a front side of a front surface 105 of the main cassette portion 101, via which a magnetic tape 107 is pulled outside, is rotatably mounted a lid member 104. The front surface 105, via which the magnetic tape 107 is pulled out, delimits a spacing for loading 105 into which is intruded a tape loading unit on the video tape recorder on which is loaded the tape cassette 100, as shown in FIG. 3. The spacing for loading 105 is usually closed by the lid member 104.
The tape cassette 100 includes the main cassette portion 101 within which are rotatably mounted a pair of tape reels 106A, 106B about which is placed the magnetic tape 107 having a width of 8 mm.
The magnetic tape 107 is pulled out from a tape reel 106A and guided by a tape guide unit, not shown, along the spacing for loading 105 by a guide mechanism, not shown, so as to be taken up on the opposite side tape reel 106B. The state of winding of the magnetic tape 107 on the tape reel 106 in the tape cassette 100 can be checked from outside via a reel window 108 provided in the upper cassette half 102, as shown in FIG. 1.
The lower cassette half 103 is provided with a pair of reel bearing holes 109A, 109B for causing hubs of the tape reels 106 housed therein to face outwards, as shown in FIG. 3. On the back surface of the lower cassette half 103 is formed a reel lock guide portion 110 intermediate between the reel bearing holes 109A, 109B, while an end detector 111 is provided on the front side of the lower cassette half 103, as shown in FIG. 3. On both corner portions on the back surface of the lower cassette half 103 are provided plural design statement detection portions 112A, 112B constituted by plural detection holes opened at pre-set positions in association with tape design statements, such as type, length or recording density of the magnetic tape 107.
Although not shown in detail, the reel lock guide portion 110 is made up of a reel lock guide groove formed in the lower cassette half 103, a reel lock member movably housed within the reel lock guide groove in the inside of the lower cassette half 103 for movement in the fore-and-aft direction, a pair of reel lock levers mounted integrally with or for rotation in unison with the reel lock member, and a reel lock spring. When the tape cassette is not in use, the reel lock guide portion 110 retains the tape reels 106A, 106B against idle rotation by the foremost part of the reel lock lever meshing with an outer peripheral tooth formed on the pouter periphery of flange portions of the tape reels 106A, 106B.
With the above-described structure of the tape cassette 100, when the cassette main portion 100 is loaded in the video tape recorder, with the bottom surface and both lateral sides of the cassette main portion 101 as reference surfaces, the reel lock member is moved against the elastic force of the reel lock spring by a reel unlocking member intruded from the reel lock guide groove. The tape reels 106A, 106B of the tape cassette 100 are released from the retained state by the reel lock lever and become rotatable.
On the other hand, the lid 104 of the tape cassette 100 is rotated by the lid opening mechanism provided on the video tape recorder for opening the spacing for loading 106. In the above-mentioned unlocked state of the tape reels 106A, 106B, the magnetic tape 107 of the tape cassette 100 is pulled out by the loading unit provided in the video tape recorder intruded via the loading for spacing 105 for defining a pre-set tape running path by way of effecting a loading operation.
A reel driving shaft 120 of the video tape recorder is intruded into reel bearing holes 109A, 109B for being engaged with hub openings formed in the tape reel 106. With reel driving shafts 120A, 120B being run in rotation by the recording or reproducing operation, the tape reels 106A, 106B of the tape cassette 100 are run in rotation for reeling out or taking up the magnetic tape 107. When the tape cassette 100 is loaded on the video tape recorder, the design statement portions 112A, 112B formed on both core portions of the lower cassette half 103 are detected by a detection mechanism, not shown.
In general, the upper cassette half 102a and the lower cassette half 102b of the tape cassette are molded of a synthetic resin material for reducing the weight. Therefore, if the small-sized tape cassette 100 having housed therein the magnetic tape 107 having a tape width of 8 mm is loaded on the video tape recorder for driving the tape, the tape cassette in its entirety is oscillated by the operation of the tape driving mechanism to render the running performance of the magnetic tape 107 instable. Since the recording/reproducing characteristics of the information signals recorded to a high recording density on the magnetic tape 107 are deteriorated by this phenomenon, the tape cassette 100 needs to be constructed to have a constant weight to eliminate adverse effects such as oscillations transmitted from the tape recording mechanism of the video tape recorder.
For overcoming such inconvenience, there is proposed a in JP Utility Model Kokai JP-A-63-38460 a tape cassette in which a cassette main body portion is constructed by securing a pre-molded synthetic resin member by an adhesive to a frame-shaped metallic member exposed to a lower cassette half by reel bearing holes. This tape cassette has such features that the overall mechanical strength is maintained against torsion or warping and that, since a portion of the cassette main body portion is formed of a metallic material, the overall weight is increased and the reel holes are improved in accuracy.
However, with the above tape cassette, since the metallic member and the synthetic resin member are secured to each other by the adhesive, the frame assembling process is complicated and involves a large number of steps, while the adhesive is laborious to handle, thus raising difficulties in production. Moreover, since the reference plane is constructed towards the metallic member, the cassette loading unit, reel unlock member, lid opening mechanism or the detection unit of the video tape recorder tend to be worn out by the loading operations of the tape cassette on the video tape recorder.
Moreover, in order for the tape cassette to be loaded correctly on the video tape recorder, the shape or interval of the reel holes or the above-mentioned various members of the cassette main body portion need to be positioned accurately relative to one another. However, since these positioning members are formed on the metallic frame to form the lower cassette half in the above-described prior-art tape cassette, it is difficult to maintain high precision of the component parts as compared to a tape cassette employing a frame formed of synthetic resin.
For overcoming such inconvenience, a tape cassette has been developed in which the basic structure of a cassette main body portion combined from a metallic member and a synthetic resin member is used, more specifically, an outer portion of the lower cassette half is formed of synthetic resin and a metallic plate is insertion-molded on the bottom plate portion of the lower cassette half. With such tape cassette, since it has a pre-set weight, the magnetic tape is allowed to run in stability without being affected by vibrations of the tape driving mechanism to permit reliable high-density recording and/or reproduction of information signals. Moreover, since the positioning portions or sliding portions of the tape cassette are formed on the synthetic resin member, there is no risk of abrasion of various engagement members of the video tape recorder.
However, with this tape cassette, because of the large differential thermal contraction ratio between the synthetic resin and the metallic plate, the force of contraction at the time of curing of the synthetic resin portion acts on the metallic plate making up a portion of the bottom plate of the lower cassette half, thus severely warping the metallic plate. This phenomenon results in a variety of problems such as incapacitated loading of the tape cassette on the video tape recorder, rotational troubles of the tape reels or inaccurate positioning of various component parts.
This inconvenience may be dealt with by using a metal plate of increased thickness and mechanical strength to prevent deformation due to thermal contraction. However, the outer size of a tape cassette is prescribed by pertinent standards, so that, if a metallic plate producing a desired effect is used, the overall thickness of the tape cassette cannot be comprised within a prescribed value.